Biological Aspects of Slow Sand Filtration: Past, Present and Future SJ. Haig*, G. Collins**, R.L. Davies*** C.C. Dorea**** and C. Quince* *School of Engineering, Rankine Building, University of Glasgow, G12 8LT, UK (E-mail:
[email protected];
[email protected];
[email protected]) **School of Natural Sciences, National University of Ireland, Galway, University Road, Galway, Ireland ***School of Infection, and Immunity, Glasgow Biomedical Research Centre, University of Glasgow, G12 8TA, UK (E-mail:
[email protected]) ***Département génie civil et génie des eaux/ Civil and Water Engineering, Université Laval, Québec (QC), Canada G1V 0A6 (E-mail:
[email protected]) Abstract For over 200 years, slow sand filtration (SSF) has been an effective means of treating water for the control of microbiological contaminants in both small and large community water supplies. However, such systems lost popularity to rapid sand filters mainly due to smaller land requirements and less sensitivity to water quality variations. SSF is still a particularly attractive process because its operation does not require chemicals or electricity. It can achieve a high level of treatment, which is mainly attributed to naturally-occurring, biochemical processes in the filter. Several microbiologically- mediated purification mechanisms (e.g. predation, scavenging, adsorption and bio-oxidation) have been hypothesised or assumed to occur in the biofilm that forms in the filter but these have not yet been comprehensively verified. Thus, SSFs are operated as “black boxes” and knowledge gaps pertaining to the underlying ecology and ecophysiology limit the design and optimisation of the technology.